The present invention relates to an endoscope having a very fine insertion section, which is able to enter, for example, a blood vessel.
A conventional endoscope comprises an insertion section which can be inserted into a body cavity, and a control section for controlling the insertion section from outside of the body cavity. The distal end of the insertion section has an illumination window incorporated therein, for illuminating the body cavity, as well as an observation window for receiving a light beam which is irradiated from the illumination window and reflected by the wall of the body cavity. Arranged within insertion section are a light guide fiber bundle for transmitting an illumination light beam emitted from an external light source, an illumination lens for diffusing the light beam transmitted through the light guide fiber bundle, an object lens for forming an image of the interior of the body cavity, based on the beam incident through the illumination window, and an image guide fiber bundle for transmitting the image formed by the object lens to outside of the body cavity. The light-emission end portion of the light guide fiber bundle is cylindrical in shape, as is the illumination lens, which faces the light-emission end portion.
The outer diameter of an endoscope insertion section able to enter a blood vessel must, as a matter of course, be very small. Therefore, if the light-emission end portion of the light guide fiber bundle is cylindrical in shape, this results in a decrease in the cross section of the end portion, with a consequent decrease in the amount of illumination light which can be transmitted therethrough.
An endoscope is known, the light-emission end of the light guide fiber bundle of which is formed as a hollow cylinder, in order to surround the object lens. In this way, the cross section of the light-emission end portion can be increased, increasing the amount of light which can be transmitted therethrough, while the outer diameter of the insertion section can be kept small. In the case of this endoscope, it is necessary that the shape of the illumination lens correspond to the shape of the light-emission end of the light guide fiber bundle. However, the formation of a hollow cylindrical illumination lens is technically difficult, inevitably resulting in high manufacturing costs.
An endoscope having a very fine insertion section is used mainly to observe narrow, confined areas such as the interior of blood vessels. In such restricted areas, the lens effect, for diffusing illumination light, is not required. Accordingly, an endoscope is known, the end face of the light guide fiber bundle of which is exposed. Having no illumination lens, such an endoscope is relatively simple in structure and can thus be manufactured at low cost.
However, this type of endoscope does have the following drawbacks:
With increasing number of patients receiving medical treatment involving the use of an endoscope, it has become ever more important to ensure that the device be thoroughly sterilized each time use is made thereof. This results in the endoscope being frequently immersed in sterilizer liquid. Over time, however, coloring and erosive substances contained in the sterilizer liquid damage the light-emisssion end face of the light guide fiber bundle, reducing the amount of light which can be emitted therefrom.
Japanese Utility Model Disclosure (Kokai) No. 61-143120/86 proposes an endoscope wherein, for example, an epoxy resin ahhesive is coated on the light-emission end face of the light guide fiber bundle, in order to protect the exposed end face thereof against the harmful effects of sterilizer liquid. In Disclosure No. 61-143120/86, the object lens projects from the end face of the light-emission end portion of the light guide fiber bundle. A stepped portion is formed between the object lens and the light guide fiber bundle, and is filled with resin, the outer face of the body of resin formed therein being made convex.
Since the resin layer used in the endoscope of Disclosure No. 61-143120/86 is of convex lens shape, this results in the resin layer being disadvantageously thick. While a number of epoxy resins and acryl resins possess a relatively high transparency, when formed as a layer, the thicker the layer is formed, the lower the degree of transparency becomes, with a consequent lowering of the light transmittance thereof. Compared to normal endoscopes, an endoscope having a very fine insertion section contains a lower number of light guide fibers. Therefore, any loss in the light transmittance of the light guide fibers of this type of endoscope represents a much more serious operating disadvantage than in the case of the conventional device.
Furthermore, epoxy, acryl, silicone resins have fluidity until they completely harden. Distortion may likely occur in a convex-lens-shaped layer made of such resins. Also, since the resin layer is exposed, the surface of the resin layer may likely be damaged by outside solid articles. If the surface of the resin layer is scarred, the light transmission degree is lowered. In the worst case, the resin layer may be detached from the endoscope.
The object of the present invention is to provide an endoscope which can overcome the problems in prior art, wherein a transparent resin layer of a uniform thickness can be formed easily and economically on an end face of a light guide fiber bundle. The resin layer has a stable strength, and is hardly damaged and detached from the endoscope.
In order to achieve the above object, the present invention provides an endoscope which comprises a small-diameter insertion section able to enter a body cavity, the insertion section having a hollow cylindrical member one end of which has an opening to the outside, said cylindrical member containing a light guide fiber bundle for emitting a beam illumination light into the body cavity, an object optical system for receiving a beam reflected from the body cavity to form an image formed, and image transmission means for transmitting the image; a recess portion having a side wall defined by said cylindrical member, a bottom wall defined by said light guide fiber bundle, and an opening at said one end of the cylindrical member; and a transparent resin layer of a uniform thickness, arranged within said recess portion and sealing the inside of said cylindrical member at said one end of the cylindrical member, said resin layer having an end face which is substantially flush with said one end of the cylindrical member.
In the present invention, one end of the sheath of the insertion section is sealed by the transparent resin layer, so that the members within the sheath are protected. Since the transparent resin layer is arranged in substantially the same plane as one end of the sheath, the resin layer can be formed easily with no special skills required. The formed resin layer is hardly damaged by external objects, and has a stable strength.